Observations

Description

Valves are disc-shaped with a flat to slightly undulate face and shallow mantle. A single fultoportula is present in a slightly eccentric position in the center valve. Areolae are present across the valve face, weakly organized into rows at the valve center and forming more distinct fascicles toward the valve margin. Fascicles are uniseriate in the valve center, and may become biseriate at the valve face/mantle interface. The number of fascicles ranges from 17-31 per valve and decreases with valve diameter. Areolae are distinct and occur at 18-20 in 10 µm. Small spines are present on each interfascicle, at the valve margin.

The relation between fascicle number and valve diameter can be expressed as total number of fascicles = 0.78 * (diameter) + 5.12. For example, measures of diameter and fascicle count, respectively, are 9.3,31; 7.4,24; 4.5,14.

Original Description

Original Description

Valves circular, almost flat 5-11 µm in diameter. Ornamentation of the valve surface consisting of barely resolvable puncta arranged in biseriate fascicles, 13-15 in 10 µm, each fascicle separated by a distance interfascicle. Each interfascicle subtended by a well developed spine. Marginal strutted processes occur directly below every 3rd to 6th spine. One eccentric strutted process on the valve face present.

Valve ornamentation occurs in a coarsely and a finely structure form. In the coarsely structured form the puncta are arranged in biseriate, straight fascicles, becoming uniseriate or disorganized towards the center of the valve. In the finely structured form the puncta are also arranged in biseriate, straight fascicles, becoming disorganized towards the center where the puncta are grouped in a rosette0like configuration.

Original Images

Cite This Page: Burge, D., and Edlund, M. (2016). Stephanodiscus parvus. In Diatoms of the United States. Retrieved February 17, 2018, from http://westerndiatoms.colorado.edu/taxa/species/stephanodiscus_parvus

Valves are small, with a flat to slightly undulate valve face. A distinct central fultoportula is eccentric to the valve center. Fascicles are composed of distinct areolae, which are uniseriate at the valve center and may biseriate at the margin. A spine is present at each interfascicle on the valve margin.

Compare

Stephanodiscus minutulus lacks a distinct central fultoportula.
Cyclostephanos invisitatus has a central annulus, higher areola density and striae are arranged in multiseriate fascicles.
Stephanodiscus binderanus grows in chains and has a deep mantle, uniseriate fascicles, a lower areola density and absence of a central fultoportula.
Stephanodiscus hantzschii and S. hantzschii f. tenuis may both be larger in diameter, lack a central fultoportula and possess multiseriate fascicles.

Links & ID's

Index Nominum Algarum (INA)

California Academy of Sciences (CAS)

NCBI Genbank Taxonomy

North American Diatom Ecological Database (NADED)

NADED ID: 64003

Autecology Discussion

Stephanodiscus parvus is most common in eutrophic lakes Erie and Ontario under conditions of high total phosphorus and moderate chloride concentration (Stoermer et al. 1978, Stoermer 1978, Stoermer and Håkansson 1984, Reavie and Kireta 2015). This taxon has also been reported from from the St. Lawrence River, with rare abundances from epilithic and epiphytic habitats, and greater abundant in sediment cores (Reavie and Smol 1998)

Images

The record of Stephanodiscus parvus in streams and rivers of the continental United States.